In robotics and bionics (including powered exoskeletons and prostheses), it is common to drive various articulating and jointed members using hydraulic piston-cylinder assemblies.
For example, the applicant's “BigDog” four-legged robot includes numerous hydraulic piston-cylinder assemblies associated with the legs of the robot. These assemblies and the associated hydraulic circuit enable the quadruped robot to walk, run, climb, traverse rough terrain, and carry heavy loads. A gasoline engine drives the hydraulic actuation system. The robot's legs articulate like an animal's legs and have compliant elements that absorb shock and recycle energy from one step to the next. The “BigDog” robot is the size of a large dog or a small mule, measuring 1 meter long, 0.7 meters tall, and weighing 75 kilograms. The robot has an on-board computer that controls locomotion, servos the legs, and handles a wide variety of sensors. The robot control system manages the dynamics of its behavior to keep it balanced, steer, navigate, and regulate energetics as conditions vary. Sensors for locomotioning include joint position, joint force, ground contact, ground load, a laser gyroscope, and a stereovision system. Other sensors focus on the internal state of the robotic system monitoring the hydraulic pressure, oil temperature, engine temperature, RPM, battery charge, and other subsystems. The robot can run at 4 mph, climb slopes up to 35 degrees, walk across rubble, and it is able to carry a 340 pound load.
The legs of this robot include, among other elements, two members, e.g., a “thigh” and a “shin” jointed at a “knee”. The thigh, in turn, is pivotally connected to the robot body at a shoulder joint. In prototype versions of the robot, one hydraulic piston-cylinder assembly is interconnected between the thigh and the shin.
The ability to walk, run, climb, and traverse rubble in a stable fashion while carrying a load is largely the result of advanced valves, advanced sensors, and computational algorithms dictating robot behaviors. High actuator speeds in the hydraulic system for the piston-cylinder assemblies requires a high flow rate for the hydraulic fluid. Increasing the load carrying capacity require large piston areas for the piston-cylinder assemblies. The combined result is a high power requirement.
With mobile manipulation and legged locomotion, it is often the case that leg movement requires, in some instances, high speed and low force while in other instances low speed and high force are required. For example, when the thigh raises the shin during walking, the force experienced on the thigh and the shin is low but the foot must travel quickly to its next position. Conversely, when the thigh lowers the shin to engage the ground, a higher force is experienced by the thigh and the shin.
To meet both requirements, a high flow rate and a large piston area are required. This results in large energy consumption when there is high flow, even when the force is low. Thus, a larger power plant is required including a larger hydraulic pump, a larger engine to run the pump, more cooling, and the like. Increasing the size and capability of the power plant, however, means the payload capacity of the robot decreases. Similar problems exist with other robots, powered exoskeletons, and prosthetic arms and legs.
Known hydraulic systems for industrial forklifts and the like are not suitable for use with robotics or bionics where a controller is used to electronically actuate the various hydraulic system valves based on a desired behavior. Still, it is useful to note the following U.S. patents incorporated herein by this reference: U.S. Pat. Nos. 3,584,536; 4,023,650; 4,258,609; 4,318,333; 4,496,033; 5,249,502; 3,824,896; 3,530,767; 4,250,805; and 4,341,105.